1. Field of the Invention
The present invention relates to an organic electroluminescent display (“OELD”), and more particularly, to a thin film transistor (“TFT”) OELD and a method of fabricating the same.
2. Description of the Related Art
Organic electroluminescent displays (“OELDs”) are self-luminescent color image displays that use an organic light-emitting diode (“OLED”). Each pixel of an OELD includes a switching (sampling) transistor for sampling an analog image signal, a storage capacitor storing an image signal, and a driving transistor controlling a current supplied to an OLED according to a voltage of the image signal stored in the storage capacitor.
Each pixel of such an OELD is divided into a region in which the switching transistor and the driving transistor are disposed, a region in which the storage capacitor is disposed, and a region in which the OLED is formed.
One problem of such an OELD is that the area of an OELD in one unit pixel must be increased to enhance the luminescent brightness.
In the case of a 2-inch quarter video graphic adapter (“QVGA”) OELD with a resolution of 320×240 pixels, the area of one sub-pixel is about 51×240 μm2. In order to increase the area of an OLED to enhance the luminescent brightness, regions other than the region in which the OLED is formed must be reduced in area. It is possible to increase the capacitance of the storage capacitor by reducing an inter-electrode gap of the storage capacitor or by using a material with a high dielectric constant. Therefore, it is possible to reduce the occupation area of the storage capacitor by changing a physical structure of the storage capacitor.
However, since the storage capacitor of the OELD is fabricated simultaneously with the switching transistor and the driving transistor, the structures and materials of the switching transistor and the driving transistor are limited. The storage capacitor has the same dielectric layer as an interlayer dielectric (“ILD”) layer formed on a gate of a thin film transistor (“TFT”) by top gate structure. A conventional OELD includes a single ILD layer. Since the single ILD layer serves to electrically separate a gate and a metal layer below and above the ILD layer respectively, it must not be excessively thin. In general, a storage capacitor of a QVGA OELD must have a capacitance of about 1 pF. Therefore, the thickness of the single ILD layer must not be excessively thin, in order to maintain the capacitance of the storage capacitor at about 1 pF.